To study epidemiological characteristics of thelazjasis, in Zunyi and surrounding areas, morphology and 18S rRNA gene sequence of Thelazia callipaeda.

The Thelazia callipaeda was collected from several hospitals, including affiliated Hospital of Zunyi Medical College and Zunyi Aerospace Hospital, in Zunyi region since 2011 to 2015. Clinical data of infected human thelaziasis, including the patients' gender, age, residence and pets such as cats or dogs, were analyzed to find out the factors influencing the incidence. Morphology characteristics of female and male Thelazia callipaeda were observed under microscope. 18S rRNA gene of Zunyi Thelazia callipaeda was amplified by PCR, and the evolutional relationship was analyzed through the software MEGA 7.01 based on neighbour-joining (NJ) method. Homology was campared with 18S rRNA gene from GenBank in National Center of Biotechnology.

Totally 25 cases had been reported during the study, of which 22 cases had more details. Based on the cases, we found the thelaziasis was increasing year by year. For instance, 2 cases (9.1%) were reported in 2011, 1 case (4.5%) in 2012, 3 cases in 2013 (13.6%), 10 cases (45.5%) in 2014 and 6 cases (27.3%) in 2015. During the five years, totally 15 cases were treated between August and November, when the human thelaziasis was in typical epidemic peaks. We analyzed characteristics of the total cases reported to date. Most of the cases occurred in rural areas (20 cases). Majority of patients lived in rural region. And most cases were between 30 to 60 years old, indicating no age limit, especially, there were two cases who were at the ages of 8.5 months and 77 years old, respectively. Moreover, more women suffered from the disease than that in men, of which, the case number was 16 in women and 6 in men, and there were 7 cases who had cats or dogs at home. Under light microscope, the edge of Thelazia callipaeda had serrated cuticle with transverse striations. And male worm had a sharp peak at the tail end of Thelazia callipaeda, which cured to the ventrite and had two copulatory spicules, long one and short one, respectively. While female worm had a blunt tail, containing numerous eggs and rounded first-stage larvaes in a single line in the distal area of the uterus, near the vulva. Sequences of Thelazia callipaeda 18S rRNA gene from Zunyi and Oita Japan (AB538282.1) were showed homology of 100%, and they were clustered in a same branch of Phylogenetic tree.

Human thelaziasis cases in Zunyi region are increasing each year, and most of the cases have occurred in rural areas. 18S rRNA gene has a high homology with sequence AB538282.1 in Thelazia callipaeda. Combining clinical data, analysis of epidemiological characteristics and the characteristics of 18S rRNA should be good for specie identification and epidemiological analysis.

Thelazia callipaeda; Epidemic characteristic; Morphology; 18S rRNA gene